1. Field of Invention
The present invention relates to a projection-type display apparatus that modulates an output light beam from a light source in response to a video signal using a modulating device such as a liquid-crystal light valve or the like and enlarges and projects the modulated light beam through a projection lens onto a screen. More particularly, the present invention relates to a projection-type display apparatus that illuminates an image forming area of the modulating device such as a liquid-crystal light valve.
2. Description of Related Art
Japanese Unexamined Patent Publication 3-111806 discloses a projection-type display apparatus that forms a modulated light beam in response to a video signal using a liquid-crystal light valve and enlarges and projects the modulated light beam onto a screen. As shown in FIG. 13, the projection-type display apparatus includes an integrator optical system 923 having two lens plates 921 and 922, for uniformly illuminating the image forming area of a liquid-crystal valve 925, as a modulating device, with light from a light source.
The single light beam emitted from a light source lamp unit 8 is split into a plurality of intermediate light beams by lenses 921a constituting the first lens plate 921, and is superimposed on the liquid-crystal light valve 925 through lenses 922a constituting the second lens plate 922.
In this projection-type display apparatus, the brightness of an image projected onto the screen will drop or the projected image suffers an outlining shadow if the image forming area of the liquid-crystal light valve 925 is not accurately illuminated. To cope with this problem, as shown in FIG. 14, a certain margin M is assured around the image forming area A of the liquid-crystal light valve 925 in view of the positioning accuracies of the liquid-crystal light valve 925 and the lens plates 921, 922 constituting the integrator optical system 923, the positional errors in the focal points of the lenses 921a, 922a of the lens plates and the positioning accuracies of the remaining optical systems disposed along the optical axis.
More particularly, the image forming area A is sized to be distinctly smaller than an illumination area B by the output light from the light source. Even if the illumination area B is offset vertically upward or downward, or horizontally leftward or rightward depending on the overall positioning accuracy of the above components, the image forming area A is designed to be kept within the illumination area B. This avoids the outlining shadow around the projected image and drop in brightness of the projected image. To cope with a large quantity of positional error of the components, the margin M is simply widened.
To increase the brightness of a projected image, the efficiency in the utilization of the light that illuminates the liquid-crystal light valve 925 needs to be increased. If the margin M is enlarged to accommodate errors of the components, the efficiency in the utilization of light drops, thereby dimming the projected image. Thus, the width of the margin formed around the image forming area of the liquid-crystal light valve is preferably narrow. A narrow margin in turn offsets the illumination area from the image forming area of the liquid-crystal light valve, possibly presenting a shadow outlining the projected image.
It is an object of the present invention to provide a projection-type display apparatus that offers an increased image brightness without any shadow around a projected image while presenting a narrow margin around the image forming area of a liquid-crystal light valve.
A first projection-type display apparatus of the present invention may include a light source, a modulating device for modulating a light beam emitted by the light source and a projection device for enlarging and projecting the modulated light beam from the modulating device onto a projection area. An optical element may be disposed in an optical path between the light source. The modulating device may split the light beam emitted from the light source into a plurality of intermediate light beams. A superimposing device may also be provided for superimposing each of the slit intermediate light beams from the optical element on an image forming area of the modulating device. The mounting position of the superimposing device may be adjustable.
This may increase the efficiency in the utilization of illumination light that illuminates the modulating device, thereby brightening a projected image. Even when the margin around the image forming area of the modulating device is narrowed, the illumination area relative to the modulating device is fine-adjusted so that the image forming area is kept within the illumination area and the projected image is free from the outlining shadow attributed to any offset between the image forming area and the illumination area.
After components of the optical systems are mounted, the image forming area of the modulating device is illuminated by the optical element and the superimposing device. When the illumination area is offset from the image forming area of the modulating device, the superimposing device is fine-adjusted so that the image forming area of the modulating device is fully included within the illumination area. Taking into consideration the offset between the illumination area and the image forming area, attributed to the positioning error of the optical components, the margin formed around the outline of the image forming area of the modulating device is narrowed.
Since the mounting position of the superimposing device, which is an optical component chiefly determining the illumination area of the modulating device, may be fine-adjusted, the position of the illumination area of the modulating device is easily and efficiently adjusted. The adjustment of the position of the illumination area is thus performed taking into consideration the overall mounting error of optical components (optical elements) in front of the superimposing device (upstream of the superimposing device in the optical path).
Since the plurality of split intermediate light beams are finally superimposed on a single illumination area through the superimposing device and are then delivered, a constant-brightness polarized light beam with no illuminance variations is obtained as an illumination light even when an incident light beam has a large light intensity distribution in its cross section. A constant-brightness polarized light beam with no illuminance variations may be obtained as an illumination light when the incident light beam has a uniform light intensity, when the intermediate light beam cannot be separated into a p-polarized light and an s-polarized light beam because of spectral characteristics, or when the light intensity and spectral characteristics change in the course of aligning the polarization directions of both polarized light beams.
The projection-type display apparatus may present a particularly bright projected image that is uniform and bright on an entire display area or projection area.
A reflection device for bending an optical path may be disposed in the optical path extending from the light source to the modulating device. If an error is introduced in the mounting angle of the reflection device, the illumination area may be offset from the image forming area of the modulating device. The mounting angle of the reflection device is such that it is preferably adjustable relative to its incident optical axis.
The projection-type display apparatus may be applied to a projection-type display apparatus for projecting a color image. More particularly, it may be applied to a projection-type display apparatus including a color separating optical system for separating an output light from the superimposing device into color light beams, a plurality of modulating devices for modulating the color light beams separated by the color separating optical system, and a color synthesizing optical system for synthesizing the color light beams respectively modulated by the plurality of modulating device. The synthesized modulated light beam from the color synthesizing optical system may be enlarged and projected through the projection device to the projection area.
In the projection-type display apparatus for projecting a color image, a reflection device may be disposed in an optical path between the color separating optical system and at least one of the plurality of modulating devices. The illumination area may be offset depending on the mounting angle of the reflection device. The reflection device may be preferably adjustable in its mounting angle with respect to the incident optical axis.
The reflection device disposed closest to the modulating device remaining adjustable in its mounting angle is advantageous from the standpoint of assembling the apparatus and position adjusting the illumination area relative to the modulating device.
If the modulating device is a reflection type modulating device and the color separating optical system and the color synthesizing optical system are integrated into the same optical system, the optical path length is shortened to result in a compact-design projection-type display apparatus.
A second projection-type display apparatus of the present invention may include a light source, a first optical element for splitting a light beam from the light source into a plurality of intermediate light beams and a second optical element comprising a polarization conversion unit and a superimposing device for superimposing light beams output from the polarization conversion unit. The polarization conversion unit may be arranged in the vicinity of a position where the intermediate light beams are converged to separate each of the split intermediate light beams from the first optical element into a p-polarized light beam and an s-polarized light beam. The polarization conversion unit may further align the polarization direction of one of the p-polarized light beam and the s-polarized light beam with the polarization direction of the other of the p-polarized light beam and the s-polarized light beam and output the resulting light beams. A modulating device may modulate the light beams emitted from the second optical element and a projection device may enlarge and project the modulated light beams from the modulating device to a projection area. The mounting position of the superimposing device may be adjustable.
The polarization conversion unit may be additionally provided besides the arrangement according to the first aspect, and thus, the second projection-type display apparatus presents the advantage offered by the use of the polarization conversion unit in addition to the advantage presented by the first projection-type display apparatus. More particularly, with the polarization conversion unit, polarizing light beams are efficiently used without wasting both light beams to thereby result in a bright projected image.
A reflection device for bending an optical path may be disposed in the optical path extending from the light source to the modulating device. The second projection-type display apparatus may be used in a projection-type display apparatus for projecting a color image. The mounting angle of the reflection device disposed closest to the modulating device may be adjustable and the modulating device may be a reflection type modulating device. Thus, the same advantages offered by the first projection-type display apparatus are achieved.
To make the mounting position of the superimposing device adjustable in the first projection-type display apparatus, an adjusting mechanism may be provided. More particularly, a first adjusting mechanism may be provided for adjusting the mounting position of the superimposing device in a first direction that is orthogonal to an optical axis. A second adjusting mechanism may be provided for adjusting the mounting position of the superimposing device in a second direction that is orthogonal to both the optical axis and the first direction.
A base adjusting plate may be provided to realize such an adjusting mechanism. Further, a first adjusting plate slidably movable in the first direction relative to the base adjusting plate and a second adjusting plate slidably movable in the second direction relative to the first adjusting plate may also be provided. With this mechanism, the mounting position of the superimposing device may be independently adjusted in individual directions (i.e., in the first and second directions).
The mounting position of the superimposing device may be difficult to adjust if the first adjusting plate is offset in the second direction when the second adjusting plate is slid in the second direction or if the second adjusting plate is offset in the first direction when the first adjusting plate is slid in the first direction. For this reason, the adjusting mechanism preferably includes a first slip prevention mechanism for preventing the first adjusting plate from slipping in the second direction and a second slip preventing mechanism for preventing the second adjusting plate from slipping in the first direction. This solves some of the above problems and the mounting position of the superimposing device is easily and accurately adjusted. When the adjusting mechanism including the first and second adjusting plates is employed, the superimposing device may be fixed to the second adjusting plate.
In the second projection-type display apparatus an adjusting mechanism may be provided to make the mounting position of the superimposing device adjustable.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description taken in conjunction with the annexed drawings, which disclose preferred embodiments of the invention.